Project I: Temporal Stability and Determinants of Outcome of Subtypes of Learning Disability brings together two of the most important components of the original research strategy: the virtues of the developmental, longitudinal design and the analytic power of the hypothesis-driven measures of the reading process used in the original Program Project Cohort. Within such a framework we propose to study what we believe is a precious resource, the cohort of 378 children recruited in the initial Program Project. This large cohort, initially assessed at 7.5-9.5 years will be systematically re-evaluated at ages 12-14 years and then, using the strategy of an extended longitudinal follow-up, examined at 6 month intervals for an additional two years at which time they will be 14-16 years of age. The sample, the measures and the longitudinal framework allow us to address four specific aims: 1) temporal stability and course over time of subgroups of learning disability (LD) and subtypes of reading disability (RD); 2) nature and determinants of outcome of specific subgroups of LD and subtypes of RD; 3) nature and determinants of plateau effects; and 4) specific hypotheses relating to the cognitive and neurolinguistic mechanisms influencing RD. Project I will examine changes in reading and systematically consider their relation to such factors as initial subtype classification, stability of different subtypes,and subtype at outcome. The frequent assessments as part of the extended longitudinal examination will also allow the use of individual growth curve models to investigate the observed variability in both the time and level at which academic skills plateau, and to examine hypotheses relating to lag versus deficit models for specific reading domains. Finally, maintaining and examining this sample from beginning reading to the time when reading should have become automatic permits the investigation of specific hypotheses relating to the development of reading and RD.